Electrophotography type of image formation apparatuses have been widely used hitherto. For example, the electrophotographic image formation apparatus has a document table made of glass for placing a source document; and forms a printed picture image (copied picture image) through the steps of projecting illumination light upward to the source document placed on the document table, electrifying uniformly a drum-shaped image-holding member (photosensitive drum) with rotation at a prescribed process speed, projecting the light carrying the image information onto the photosensitive drum to form electrostatic latent image, developing the electrostatic latent image by use of a development unit to form a developed image, and transferring the developed image onto a recording medium to obtain a printed image (copied image).
In one type of image formation apparatus, a photosensitive drum and a development unit are placed with a prescribed spacing (e.g., 0.3 mm) and a developing agent is supplied from the development unit to the photosensitive drum to develop an electrostatic latent image. This development unit is usually incorporated demountably into the body of the image formation apparatus.
In the image formation apparatus having such a construction, the development unit is demounted from the main body of the apparatus for replenishment of the developing agent, and is incorporated again into the main body after the replenishment. In the operation of incorporation of the development unit, if the development unit is pushed into the main body vigorously, the development unit can collide against the photosensitive drum regardless of the designed spacing (aforementioned prescribed spacing) between the development unit and the photosensitive drum. The collision of the development unit against the photosensitive drum may impair the photosensitive drum and the development unit to hinder the image formation.